1. Field of the Invention
The present invention relates to a pipe sweeper adapted for cleaning the inside of a pipe by removing scales accumulated in the pipe and/or oxide films which may be left in the pipe around a weld of the pipe. More particularly, the present invention pertains to a pipe sweeper having pins which are adapted to be engaged with the inside surface of the pipe to thereby remove the scales and/or oxide films accumulated in the pipe. Specifically, the present invention is directed to an improvement of the pins of such pipe sweepers.
2. Description of the Prior Art
The U.S. Pat. No. 4,244,073 discloses a sweeper or a pig which is adapted to be propelled in a pipe under a water pressure for removing scales and/or slugs accumulated on the inner surface of the pipe. The sweeper has a body which is of a cylindrical configuration and made of a resilient material such as a foamed polyurethane. A plurality of pins are embedded to the body to project in radial directions. The pins are adapted to be engaged with the inner surface of the pipe and are made of a metallic material having a hardness which is a little higher than the hardness of the material constituting the pipe. Usually, the pins have a hardness in Brinell scale of approximately 150 to 160. The pin has a head which is provided with an edge portion for engagement with the inner surface of the pipe. Below the head, there is an anchor portion which is adapted to be driven into the body.
The sweeper body has a diametrical dimension which is slightly larger than the inner diameter of the pipe and water pressure is applied to the back side of the pipe to propel the body. The pins projecting radially outward from the body are forcibly engaged with the inner surface of the pipe to remove the scales and/or slugs. In operation, water spouts out forward through spaces which are formed between adjacent pairs of the pins from the space in the pipe behind the sweeper to the space ahead of the sweeper. The scales and/or slugs removed from the pipe are then carried by the water stream to be expelled from the pipe.
In this type of sweeper, it is expected that the head of each pin makes a surface contact with the inner surface of the pipe to provide the expected result of removing scales and/or slugs. However, in actual practice, it has been experienced that the pins incline rearward during the operation. This tendency is caused by the fact that the pins are forced to engage the inner surface of the pipe under a substantial pressure so that the pins tend to resist the propelling force applied by the water pressure. Usually, the head portions of the pins are of a rectangular configuration and the front corner edge engages with the inner surface of the pipe if the pins are thus inclined. The aforementioned tendency of rearward inclination of the pins therefore causes an accelerated wear of the front edge of the pin so that the pin will soon be worn at the front edge portion to such an extent that it makes a surface contact with the inner surface of the pipe in inclined positions.
A sweeper of this type is often used for scale removal at welded portions of a pipe. In this instance, the sweeper has to be driven back and forth to clean the opposite sides of the weld beads. However, if the pins are worn only at the front edges as previously described, it will become difficult to clean the back side of the weld bead by driving the sweeper in the reverse direction because in this direction surface contact can no longer maintained. Since the pins are relatively expensive, it not advantageous to replace such partly worn pins with new ones.